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reflectlite: remove stringHeader #5389

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reflectlite: remove stringHeader #5389

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10 changes: 2 additions & 8 deletions src/internal/reflectlite/type.go
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Original file line number Diff line number Diff line change
Expand Up @@ -453,10 +453,7 @@ func rawStructFieldFromPointer(descriptor *structType, fieldType *RawType, data
data = unsafe.Add(data, 1) // C: data+1
tagLen := uintptr(*(*byte)(data))
data = unsafe.Add(data, 1) // C: data+1
tag = *(*string)(unsafe.Pointer(&stringHeader{
data: data,
len: tagLen,
}))
tag = unsafe.String((*byte)(data), tagLen)
}

// Set the PkgPath to some (arbitrary) value if the package path is not
Expand Down Expand Up @@ -930,10 +927,7 @@ func readStringZ(data unsafe.Pointer) string {
data = unsafe.Add(data, 1) // C: data++
}

return *(*string)(unsafe.Pointer(&stringHeader{
data: start,
len: len,
}))
return unsafe.String((*byte)(start), len)
}

func (t *RawType) name() string {
Expand Down
50 changes: 15 additions & 35 deletions src/internal/reflectlite/value.go
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Original file line number Diff line number Diff line change
Expand Up @@ -713,20 +713,12 @@ func (v Value) Slice(i, j int) Value {

case String:
i, j := uintptr(i), uintptr(j)
str := *(*stringHeader)(v.value)

if j < i || str.len < j {
slicePanic()
}

hdr := stringHeader{
data: unsafe.Add(str.data, i),
len: j - i,
}
str := *(*string)(v.value)
sliced := str[i:j]

return Value{
typecode: v.typecode,
value: unsafe.Pointer(&hdr),
value: unsafe.Pointer(&sliced),
flags: v.flags,
}
}
Expand Down Expand Up @@ -801,7 +793,7 @@ func (v Value) Len() int {
case Slice:
return int((*sliceHeader)(v.value).len)
case String:
return int((*stringHeader)(v.value).len)
return len(*(*string)(v.value))
default:
panic(&ValueError{Method: "Len", Kind: v.Kind()})
}
Expand Down Expand Up @@ -977,13 +969,10 @@ func (v Value) Index(i int) Value {
// Keeping valueFlagExported if set, but don't set valueFlagIndirect
// otherwise CanSet will return true for string elements (which is bad,
// strings are read-only).
s := *(*stringHeader)(v.value)
if uint(i) >= uint(s.len) {
panic("reflect: string index out of range")
}
s := *(*string)(v.value)
return Value{
typecode: uint8Type,
value: unsafe.Pointer(uintptr(*(*uint8)(unsafe.Add(s.data, i)))),
value: unsafe.Pointer(uintptr(s[i])),
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@eliasnaur eliasnaur May 11, 2026 •
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Shouldn't this be unsafe.Pointer(uintptr(&s[i]))? Also, can the uintptr intermediate cast be replaced with unsafe.Pointer(unsafe.StringData(s[i:]))?

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@aykevl aykevl May 11, 2026 •
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No. It's a string index operation (not a slice operation), so it returns the byte at the given index in the string. Since it's just a single byte, it's stored directly in the Value.value field.

flags: v.flags & valueFlagExported,
}
case Array:
Expand Down Expand Up @@ -1714,8 +1703,7 @@ const zerobufferLen = 32
func init() {
// 32 characters of zero bytes
zerobufferStr := "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"
s := (*stringHeader)(unsafe.Pointer(&zerobufferStr))
zerobuffer = s.data
zerobuffer = unsafe.Pointer(unsafe.StringData(zerobufferStr))
}

func Zero(typ Type) Value {
Expand Down Expand Up @@ -1766,19 +1754,11 @@ type sliceHeader struct {
cap uintptr
}

// Like sliceHeader, this type is used internally to make sure pointer and
// non-pointer fields match those of actual strings.
type stringHeader struct {
data unsafe.Pointer
len uintptr
}

// Verify SliceHeader and StringHeader sizes.
// Verify SliceHeader size.
// See https://github.com/tinygo-org/tinygo/pull/4156
// and https://github.com/tinygo-org/tinygo/issues/1284.
var (
_ [unsafe.Sizeof([]byte{})]byte = [unsafe.Sizeof(sliceHeader{})]byte{}
_ [unsafe.Sizeof("")]byte = [unsafe.Sizeof(stringHeader{})]byte{}
)

type ValueError struct {
Expand Down Expand Up @@ -1845,29 +1825,29 @@ func Copy(dst, src Value) int {

func buflen(v Value) (unsafe.Pointer, uintptr) {
var buf unsafe.Pointer
var len uintptr
var length uintptr
switch v.typecode.Kind() {
case Slice:
hdr := (*sliceHeader)(v.value)
buf = hdr.data
len = hdr.len
length = hdr.len
case Array:
if v.isIndirect() || v.typecode.Size() > unsafe.Sizeof(uintptr(0)) {
buf = v.value
} else {
buf = unsafe.Pointer(&v.value)
}
len = uintptr(v.Len())
length = uintptr(v.Len())
case String:
hdr := (*stringHeader)(v.value)
buf = hdr.data
len = hdr.len
s := *(*string)(v.value)
buf = unsafe.Pointer(unsafe.StringData(s))
length = uintptr(len(s))
default:
// This shouldn't happen
panic("reflect.Copy: not slice or array or string")
}

return buf, len
return buf, length
}

//go:linkname sliceGrow runtime.sliceGrow
Expand Down
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